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Toward a Quantitative Description of Large Scale Neocortical Dynamic Function and EEG

Nunez, Paul L. (2000) Toward a Quantitative Description of Large Scale Neocortical Dynamic Function and EEG.

Short Abstract:

A general conceptual framework for large-scale neocortical dynamics based on data from many laboratories is applied to a variety of experimental designs, spatial scales and brain states. and mathematical theories, but includes experimental predictions from both inside and outside EEG. Partly distinct, but interacting local processes (eg, neural networks) arise from functional segregation. Global processes arise from functional integration and can facilitate (top down) synchronous activity in remote cell groups that function simultaneously at several different spatial scales. Simultaneous local processes may help drive (bottom up) macroscopic global dynamics observed with EEG (or MEG). A local/global dynamic theory is outlined that is consistent with EEG data and the proposed conceptual framework.. The theory is neutral on properties of neural networks, embedded within macroscopic fields. Nevertheless, the purely global part of the theory makes several qualitative and semi-quantitative predictions of EEG measures of traveling and standing wave phenomena. A more general "meta-theory" also suggests what large-scale quantitative theories of neocortical dynamics may be like when more accurate treatment of local and non-linear effects is achieved. The theory describes the dynamics of fields of excitatory and inhibitory synaptic action fields. EEG and MEG provide large-scale estimates of modulation of these synaptic fields about background levels. Brain states are determined by neuromodulatory control parameters. Purely local states are dominated by local feedback gains and rise and decay times of post-synaptic potentials. Dominant local frequencies vary with brain region. Other states are purely global, with moderate to high coherence over large distances. Multiple global mode frequencies are due to a combination of delays in cortico-cortical axons and neocortical boundary conditions. Global frequencies are identical at all cortical regions. But most states are local/global, involving dynamic interactions between local networks and the global system. Observed EEG frequencies may involve "matching" of local resonant frequencies with one or more of the multiple, closely spaced global frequencies.

Long Abstract:

A general conceptual framework for large-scale neocortical dynamics based on data from many laboratories is applied to a variety of experimental designs, spatial scales and brain states. and mathematical theories, but includes experimental predictions from both inside and outside EEG. Partly distinct, but interacting local processes (eg, neural networks) arise from functional segregation. Global processes arise from functional integration and can facilitate (top down) synchronous activity in remote cell groups that function simultaneously at several different spatial scales. Simultaneous local processes may help drive (bottom up) macroscopic global dynamics observed with EEG (or MEG). A local/global dynamic theory is outlined that is consistent with EEG data and the proposed conceptual framework.. The theory is neutral on properties of neural networks, embedded within macroscopic fields. Nevertheless, the purely global part of the theory makes several qualitative and semi-quantitative predictions of EEG measures of traveling and standing wave phenomena. A more general "meta-theory" also suggests what large-scale quantitative theories of neocortical dynamics may be like when more accurate treatment of local and non-linear effects is achieved. The theory describes the dynamics of fields of excitatory and inhibitory synaptic action fields. EEG and MEG provide large-scale estimates of modulation of these synaptic fields about background levels. Brain states are determined by neuromodulatory control parameters. Purely local states are dominated by local feedback gains and rise and decay times of post-synaptic potentials. Dominant local frequencies vary with brain region. Other states are purely global, with moderate to high coherence over large distances. Multiple global mode frequencies are due to a combination of delays in cortico-cortical axons and neocortical boundary conditions. Global frequencies are identical at all cortical regions. But most states are local/global, involving dynamic interactions between local networks and the global system. Observed EEG frequencies may involve "matching" of local resonant frequencies with one or more of the multiple, closely spaced global frequencies.

Keywords:	EEG, neocortical dynamics, standing waves, functional integration, spatial scale, binding problem, synchronization, coherence, cell assemblies, limit cycles, pacemakers
Subjects:	Psychology: Cognitive Psychology Computer Science: Neural Nets Neuroscience: EEG and Brain Imaging Neuroscience: Neural Modelling
ID code:	bbs00000508
Deposited by:	Paul L Nunez on 02 May 2001